Englewood's problem is it's too low density. A primarily residential and retail neighborhood would be fine if it were much much denser than Englewood. Offices are a shortcut to urban vitality because a 10-story office building is denser (ie it adds more people) than a 10-story apartment building. But you can achieve the same densities without office and still get good vitality, though not as well-spread throughout the day. That said, it doesn't appear Denver is willing to accept the residential density you'd need for that.
Anyway, for the record,
CBRE's Denver office market report tells me the region has "modest positive net absorption," and vacancy rates in Cherry Creek and Colorado Blvd are slightly better than downtown or the regional average. So I'll concede that point, although I will be surprised if it's still true in 10 years.